1. Field of Invention
The present invention relates to a method and an arrangement for automatic bow adjustment for a venetian blind assembly machine.
2. Background Art
The production of venetian blinds of different sizes and types in venetian blind assembly machines is previously known in the art. Strip material from which venetian blinds are made is typically supplied in rolls or coils at one end of the machine. The leading end of the strip of material is fed through a levelling station, where offset rollers are positioned to receive the strip material and reversibly bend the material to remove the innate bend that results from storage in a coil condition. Subsequently, the strip material passes through a forming section where mating concave and convex upper and lower form rollers create a transverse curvature in the strip material. Further on in the line of the assembly machine, slats are punched and cut from the strip material, whereafter they are fed to a lacing station, in which the slats are fed into the gaps between the vertical cords of a venetian blind cord ladder.
The object of the levelling station is to remove the innate bend of the strip material that results from storage in a coiled condition and to produce substantially straight longitudinal slats for the blind. The extent of reverse bending of the strip material in the levelling station depends on parameters such as the dimensions for the blind. Different sizes of slat width and even different colours of blinds require different degree of reverse bending. Insufficient bending or over-bending of the strip material will have the result that the slats produced from the strip material have a bow in the longitudinal direction, either provided with an xe2x80x9cupbowxe2x80x9d curvature or a xe2x80x9cdownbowxe2x80x9d curvature, lying outside acceptable predetermined deviations. According to the prior art production of venetian blinds, the bow adjustments have been done more or less xe2x80x9cmanuallyxe2x80x9d (that is, not automatically), by trial and error. The basic adjustment, as well as the continuous adjustment during production, of the levelling station has been based on experience. During production, adjustments have been carried out continuously by visually controlling if there is a bow of the slats lying outside the predetermined deviations and thereafter manually adjusting the levelling station for such deviations.
The manual adjustment of the levelling station leads to a large waste of strip material, since produced slats with an unacceptable bow must be rejected and the line must be emptied of strip material. In addition, manually adjusting the process is inefficient and time consuming, as the production must be stopped and restarted during the adjustments. The manual adjustment is especially inefficient when there is a change of dimensions or colours of the slats for production of a new blind in the machine.
Therefore, it is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art and to achieve less wastage of the strip material. A further object is to achieve a venetian blind assembly machine, which operates more efficiently and can be easily controlled to an increasing extent with respect to what is known in the art. Yet a further purpose is to achieve an economically favourable production of venetian blinds and to minimise the drawbacks of prior art processes.
The above mentioned problem has been solved with the present invention by providing a method for automatic bow adjustment for a venetian blind assembly machine. The bow adjustment station comprises rollers for guiding, bending and levelling a strip material. Further, it comprises a forming section where mating concave and convex upper and lower form rollers are arranged for creating a transverse curvature in the strip material. In addition it includes the steps of: providing levelling through means for offsetting in order to straighten the bow of the strip material within a predetermined deviation on a predetermined length of strip material; measuring the deviation through optical means providing a deviation signal; and adjusting the levelling by said means for offsetting through the deviation signal, if said measured deviation exceeds a predetermined deviation value, in order to keep the deviation within said predetermined deviation value.
An advantage with the method of the present invention is that the bow adjustment is better controlled and the manual bow adjustment can be completely avoided. Thus, the adjustments can be accomplished with an increasing rapidity when there is a change of the dimensions and the colours of the strip material in the production.
A further advantage with the method of the present invention is that a decreased wastage of strip material is obtained. Hence, a much more cost efficient production of venetian blinds can be achieved.
In addition, the present invention also relates to an arrangement for automatic bow adjustment for a venetian blind assembly machine. The bow adjustment station comprises rollers for guiding, bending and levelling a strip material. Further, it comprises a forming section where mating concave and convex upper and lower form rollers are arranged for creating a transverse curvature in the strip material. In addition it includes: means for offsetting strip material, providing levelling in order to straighten the bow of the strip material within a predetermined deviation on a predetermined length of strip material; means for optically measuring the deviation, providing a deviation signal; and means for adjusting the levelling by said means for offsetting through the deviation signal, if said measured deviation exceeds a predetermined deviation value, in order to keep the deviation within said predetermined deviation value.
Embodiments of the present invention are described, without restricting the scope of the present invention thereto with reference to the accompanying drawings, in which: